How is it possible for two parents without hitchhikers thumb to have an offspring with hitchhikers thumb?

Hitchhiker's thumb is a trait associated with a specific genetic variation, typically considered a recessive trait. If both parents carry one recessive allele for hitchhiker's thumb (heterozygous for the trait), they can pass this allele to their offspring. When the child inherits the recessive allele from both parents, they will express the trait, even though neither parent exhibits it. Thus, it's possible for two parents without the trait to have a child with hitchhiker's thumb if they are both carriers of the recessive gene.